1. Field of the Invention
This invention relates to pipe casting machines for centrifugally casting metal pipe, and more particularly to such pipe casting machines having improved intermediate mold support means for centering and supporting the pipe mold in the casting machine for rotation about its longitudinal axis.
2. Description of the Prior Art
Pipe casting machines for centrifugally casting metal pipe, typically from cast iron, are well known and widely used commercially. In such pipe casting machines, a measured amount of molten metal is poured into an elongated generally cylindrical metal mold progressively from one end thereof to the other while the mold is being rotated about its longitudinal axis at a rate to evenly distribute and retain the molten metal over the interior wall of the mold. During pouring of the molten iron and for a predetermined time thereafter, the external wall of the mold is cooled to prevent damage to the mold and to extract heat of fusion from the molten metal. This cooling is accomplished either by directing a spray or multiple streams of water onto the external surface of the mold or by submerging the mold in a cooling water bath. In either case, the mold must be cooled uniformly to avoid damage to the pipe being cast and to prevent excessive distortion of the mold.
The high speed rotation required of a centrifugal casting mold makes it necessary that any eccentric loading resulting from mold bending or being out of round be maintained at a minimum since any eccentric loading not only places uneven stresses on the equipment but also tends to produce uneven metal thickness in the pipe being cast. Any eccentric loading produced by uneven distribution of the molten metal being cast can also result in mold distortion which may further aggravate the problem. This is particularly true for relatively long molds used to cast smaller diameter pipe since the relatively slender lightweight mold structure has less rigidity in bending.
In one centrifugal pipe casting machine manufactured by Pont-a-Mousson S.A., intermediate mold stabilizing rings are provided between the external surface of the pipe mold and the rotating cylindrical casting machine having a sleeve surrounding the mold. In this machine, cooling water flows into the annular space between the rotating housing and the pipe mold mounted concentrically therein through an inlet at one end of the housing, then along the length of the mold between the mold and the housing to an exit at the opposite end of the assembly. The intermediate stabilizing or centering ring assemblies each consist of two substantially semicircular ring halves having a radial tongue on their inner diameter which fits into an annular groove in the outside diameter of the pipe mold. The outside diameter of the ring halves have a machined recess that is hardened and serves as a seat for an endless coil or garter spring which holds the split ring firmly against the mold. The outside diameter of the garter spring is sized to have a close tolerance fit within the inside diameter of the rotating housing structure and the cooling water flowing through the chamber between the mold and housing can flow over the split ring through the open coils of the spring. When a smaller diameter pipe is being cast, the ring halves may have radially inwardly extending flanges with axial bores formed therein to provide additional water flow passage. The split ring centering assemblies provide a radial load carrying support for transferring loads between the outside diameter of the mold and the larger diameter rotating sleeve or housing assembly to stabilize the rotating mold.
In the known split ring intermediate mold support design discussed above, the close tolerance fits required between the pipe mold and the split ring, the split ring and coil spring, and between the coil spring and the rotating sleeve are difficult to achieve and to maintain. Unavoidable movement of the spring relative to the split ring OD and to the rotating sleeve causes wear on the contact surfaces and when the wear becomes excessive, the mold may vibrate and/or run eccentric with respect to the axis of rotation of the assembly. This, in turn, can result in scrap pipe, and the sleeve or rings may have to be replaced. Further, wear and problems in maintaining the proper fit causes difficulty in assembly and disassembly of the pipe mold and the rotating sleeve. Accordingly, it is a primary object of the present invention to provide a centrifugal pipe casting machine having improved mold stabilizing means disposed between the mold and the casting machine housing.
Another object is to provide a centrifugal pipe casting machine with an improved split ring mold stabilizing assembly having greater dimensional tolerances and which does not require hardening the external surface of the split ring to reduce wear during use.
Another object is to provide such a pipe casting machine employing split ring type intermediate mold stabilizing assemblies which are more economical to produce, which facilitate assembly and disassembly of the pipe mold and rotating sleeve, and which require less maintenance during use.
Another object of the invention is to provide such an improved split ring intermediate stabilizing assembly which reduces mold vibration and increases stability and which provides a longer life than the known intermediate mold stabilizing assemblies.